Motor vehicle pneumatic tires must satisfy various requirements on the road. For example, wear, in particular of the tread, plays an important role in terms of the durability of the tire, but also in terms of environmental pollution. Harsh road surfaces, potholes, pebbles and sharp stones, in particular in the case of truck tires with frequent or occasional off-road use, can in some cases lead to sudden crumbling and thus to greater loss of material, so-called “chip & chunk”. Cracks and holes in the tread normally propagate radially inwards as a result of the tangential forces during vehicle operation and can then reach the belt. This consequently has the result that the steel of the belt package of a truck tire corrodes and thus becomes less stable. The aim is to make tires last longer, and thus ultimately to increase safety on the road, by a suitable construction and a rubber mixture in the tread that is as resistant as possible to wear and chip & chunk.
The wet braking behavior is additionally particularly important for safety on the road. To that end, the tire, and in particular the rubber mixture of the tread, must absorb the energy as quickly as possible upon braking, that is, must exhibit as high an absorption as possible. During vehicle operation, however, high absorption is not desirable because it increases the rolling resistance and thus the fuel consumption, which brings with it disadvantages in terms of ecology and economy.
It is known among experts that an improvement in one tire property is accompanied by the impairment of another. A so-called trade-off exists, for example, as described, between wet braking and rolling resistance. There can be a further trade-off in respect of a tread mixture between the wear resistance and the rolling resistance or the resistance to chip & chunk. For high wear resistance, a rubber mixture having a high Shore hardness is conventionally chosen. If this increased Shore hardness is established by way of a larger amount of filler, then the rolling resistance of the tire increases. If a higher Shore hardness is achieved by adjusting the network, then the resistance to crack formation and crack propagation diminishes, in particular in the case of spontaneous sudden loads which, owing to the high forces on the tire during vehicle operation, lead to the above-described phenomenon of chip & chunk.
In order to satisfy these requirements and achieve a very good performance and durability of the tire, a plurality of different types of rubber are often used in a blend in a tread mixture, for example. This presents the challenge that different polymers do not dissolve in one another completely or even only to a very small extent. In the case of a blend of two polymers, this has the result that one polymer forms a continuous phase while the other is distributed in small domains in the continuous phase. If these local phase separations are not distributed very finely and homogeneously, the above-described tire properties are generally at a poorer level.
It is known that an improvement in the homogeneity of rubber mixtures comprising different polymers in a blend can be achieved by adding additives. Many of the processing additives that are used are modified hydrocarbon resins.
JP 3714750 B discloses a rubber mixture which comprises 100 phr of a diene rubber having a glass transition temperature of from −35 to 0° C. and a hydrocarbon resin having C5 to C9 fractions and a glass transition temperature (Tg) of from 5 to 100° C. In the tire, this mixture exhibits an improved grip performance and thus better acceleration and braking properties.
From U.S. Pat. No. 8,318,861 there is known a rubber mixture which comprises an indene-based resin as the C9 fraction having an indene content of from 30 to 80 percent by mass and a softening point of from 130 to 190° C. There is used inter alia the resin obtainable under the trade name NOVARES® TN 170 having a glass transition temperature (Tg) of 120° C.
US 2011/0190416 A1 discloses a rubber mixture with improved grip on ice, and thus improved acceleration and braking behavior on ice. This mixture can comprise inter alia from 3 to 60 phr of a C9 hydrocarbon resin having a glass transition temperature of greater than 20° C. 10 phr of a resin having a Tg of 72° C. are preferably used.
US 2008/0009564 A1 discloses a rubber mixture which comprises as plasticizer system from 5 to 35 phr of MES (mild extraction solvate) or TDAE (treated distillate aromatic extract) oil and from 5 to 35 phr of a copolymer resin of a C5 fraction and a vinyl aromatic fraction. The latter can be a C9 fraction; styrene (C7 fraction) is preferred. The glass transition temperature of these resins is greater than 20° C. The rolling resistance, wet grip and chip & chunk performance of the rubber mixture are improved.
It is a common feature of all the documents that they do not contain further details regarding the wear behavior of the respectively mentioned rubber mixtures.